All police knew about the murdered teen whose body was dumped in Germantown a week ago today was written on his shirt: Roxborough High School.

With no identification on him, police went to the school the next morning and pored over the absentee list, looking for a missing student who matched the description of their victim, sources said.

Meanwhile, Patsy Foster had spent the night calling her son, Christopher, then all morning calling hospitals after he didn't return from a quick trip to a sandwich shop with a friend.

"I was getting ready to call police Thursday when they knocked on the door and said they found him," she said. "I said, 'Is he OK?' He wasn't."

Christopher Foster, 18, was found with a single gunshot wound to his torso on Woodlawn Street near Morris at 8:16 p.m. Jan. 19, said Homicide Sgt. Ron McClane. Patsy Foster said her son was also beaten around the head and face.

Police said his body was dumped in the street, but it's unknown where or why he was killed.

"We don't know if it's a robbery, a setup or what," McClane said. "We're just trying to find out what could have possibly happened and where it happened."

Foster said her son left her Roxborough home about 8 p.m. with a friend he's known since grade school to pick up a sandwich.

She said Christopher's friend later told her that they had just left the house when somebody pulled up in a car with a shotgun, and he and Christopher ran in opposite directions. Christopher's body was found just 16 minutes later.

Patsy Foster said neither she nor her other son, who were both home, heard any screams or shots.

She said she can't think of a reason anyone would want to hurt her son, whom she described as "an old soul." She had just bought him a keyboard for Christmas so he could explore his love of music, which ranged in interest from opera to rap and from Johnny Cash to Celine Dion, she said.

She hopes anyone who knows something about the crime will step forward.

"It's not like it was 1 or 2 in the morning - it was 8 o'clock," she said. "It really hurts my heart to imagine what the last thing he saw was and to know that I wasn't there to help him."

Tipsters can call homicide detectives at 215-686-3334.